This invention relates to a method of manufacturing a lighting unit which is preferably used when a product inspection is conducted by means of reflected light emitted by the lighting unit.
As a method for examining a surface of a product it has generally been known that a product to be examined is irradiated by a lighting unit through its underside and then the reflected light is visually inspected or taken a photo in close proximate to the lighting unit. If there exists some unevenness in light intensity on the surface to be examined, it may happen that a micro flaw or a finishing defect on the surface of the product to be examined is failed to be detected. Therefore, in order to examine a surface of a product it is very popular to use a lighting unit having such an arrangement that a plurality of illuminants such as light-emitting diodes are placed all over the underside of the lighting unit and the whole underside thereof emits light areally so as to keep the light intensity on the surface to be examined even. Especially in case that a product to be examined is three-dimensional, it is necessary to light up the product to be examined from not only one direction but also several directions as if to cover the product. In such a case it is usual to use a lighting unit having such an arrangement that the underside of the lighting unit, namely the surface which emits light is a concave face of a hollow truncated cone shape and that a plurality of illuminant are arranged on the concave face.
However, if a lighting unit has the above-mentioned arrangement, in order to place a plurality of illuminants all over the underside of the lighting unit, complicated steps have to be taken, such as to process the underside of the lighting unit to form a concave face of a hollow truncated cone or a hollow conic, to perforate a plurality of holes on the concave face, to embed illuminants in each of the holes respectively, and then to wire each of the illuminants by hand. This makes it difficult to assemble the lighting unit having the above-mentioned arrangement, thereby taking longer time to assemble the lighting unit. This also makes it difficult to standardize a process of manufacturing a variety of lighting units having different angle of emitting light because every step such as processing the underside of the lighting unit or the angle of a hole perforated varies.
It is an object of the present invention to provide a method of manufacturing a lighting unit characterized by that the lighting unit having such an arrangement that a plurality of illuminants are set up on a concave face of a hollow truncated cone shape can easily be manufactured.